This invention relates to vehicle control devises which provide the so-called "limp home" function for an automotive vehicle upon emergency (i,e., upon an occurrence of failure of the control driving system of the throttle valve of a multi-cylinder engine), with which the multi-cylinder engine with a linkless throttle control system can be controlled by means of the operation of the acceleration pedal even upon an occurrence of failure.
Conventionally, the output power of the engine of a vehicle is controlled by the driver by means of the acceleration pedal which is mechanically coupled to the throttle valve of the engine, In the came of the so-called linkless throttle control system, however, no mechanical connection exists between the acceleration pedal and the throttle valve, and the position of the throttle valve is controlled by a throttle actuator in response to a control signal supplied from a throttle valve control unit. The control signal is based on the operating condition of the vehicle as well as the position of the acceleration pedal. The output power of the engine can thus be adjusted not only in a accordance with the depression of the acceleration pedal but also in accordance with the operating condition of the vehicle.
FIG. 20 is a partially cut-away perspective view of a throttle body with a conventional emergency throttle operating system, which is disclosed in Japanese Laid-Open Patent (Kokai) No. 63-109244. In FIG, 20, a throttle body 1 is coupled to the air-intake system of the engine to regulate the amount of air taken into the engine. The throttle body 1 includes an air-intake pipe 3, a throttle valve 5 disposed in the air-intake pipe 3, a throttle actuator 7 for opening and closing the throttle valve 5 via a throttle shaft 13. The emergency throttle operating members include an arm 9 detachably attached to the throttle shaft 13, and an operating member 11 engaged with the arm 9.
The throttle valve 5 is fixed to the throttle shaft 13 by means of screws 15. The throttle shaft 13 is coupled to the throttle actuator 7 at one end thereof. The other end of the throttle shaft 13 extends through the throttle position sensor 17 and is urged by a return ,spring 19 toward the idle (i.e., closed) position thereof. At the extreme end of the throttle shaft 13 is formed an attachment portion 21 to which the arm 9 is attached.
The throttle actuator 7, made of a stepping motor, etc., rotates the throttle shaft 13 between the idle and the open position in response to an electrical signal from a controller. The throttle position sensor 17, consisting of a capacitor supported on the throttle shaft 13 and a contact resistor, detects the throttle position and supplies the throttle position signal to the controller. The throttle position is controlled by means of the throttle position sensor 17 and the throttle actuator 7 by a well-known method. The return spring 19 urges the throttle shaft 13 to the idle position where the throttle valve 5 is completely closed. Thus, when the throttle actuator 7 fails, the throttle valve 5 is closed by the return spring 19. The return spring 19 this serves as a fail-safe member and prevents the vehicle from running out of control.
An elongated plate-shaped arm 9 is coupled at the central engagement hole 23 thereof to the attachment portion 21 formed at the end of the throttle shaft 13. At the two ends of the arm 9 are formed engagement grooves 25 which are to be engaged with the throttle valve operating member 11, and, adjacent to the engagement grooves 25 upon the arm 9 are attached a pair of trough-shaped guide members 27. The throttle valve operating member 11 consists of a pair of strings 29 and a handle 31 fixed to the strings 29. Engagement members 33 are secured to the front end of the strings 29.
Next, the operation of the throttle body of FIG. 20 is described. Under normal driving condition, the are 9 and the operating member 11 are detached from the throttle shaft 13. Under this circumstance, the position of the throttle valve 5 is adjusted by the throttle actuator 7 on the basis of the output of the throttle position sensor 17, in response to a control signal from an exterior control unit. The control follows the well-known feedback control method.
When, on the other hand, the normal operation of the throttle valve 5 ceases due to the failure of the throttle control unit or the throttle actuator 7, the throttle valve 5 is closed to the idle position and the vehicle is temporarily stopped. Thereafter, the driver of the vehicle attaches the arm 9 of the throttle operating masher 11 to the attachment portion 21 of the throttle shaft 13 as shown by arrow A, and then, as shown by the arrow B, screws in the fixing nut 35 upon the thread 37 form on the attachment portion 21, such that the arm 9 is fixedly secured to the attachment portion 21.
The engagement members 33 at the ends of the strings 29 extending thresh the respective guide members 27 are engaged with the respective engagement grooves 25 of the arm 9, as shown by the arrows C and D. When the emergency throttle operating members are thus attached to the throttle body 1, the handle 31 is positioned within the passenger compartment, The driver of the vehicle turns the handle 31 in the direction of the arrow E or F, thereby rotating the throttle shaft 13 via the strings 29 and the arm 9 to open or close the throttle valve 5. Thus even upon an occurrence of a failure in the throttle valve drive system, a limited drivability is provided and the vehicle can be driven to a garage for repair.
The above emergency throttle operating method, however, has the following disadvantage. Normally, the emergency throttle operating members are detached from the throttle body. Thus, the emergency throttle operating members must be attached by the driver upon emergency. Further, the position of the throttle valve must be adjusted by hand using the operating member 11, rather than by kicking the acceleration pedal by the foot. The driving of the vehicle thus becomes burdensome and difficult.
FIG. 21 is a block diagram showing the overall structure of another conventional vehicle control device, which is disclosed, for example, in Japanese Laid-Open Patent (Kokai) No. 1-286837. In FIG. 21, a four-cylinder engine 111 is provided with injectors 112 and ignition plugs 113 for respective cylinders. In the air-intake pipe 3 is disposed a throttle valve 5 which is driven by a throttle actuator 7 via a throttle shaft 13. The throttle actuator 7 is made of a DC motor or a stepping motor. A return spring 19 urges the throttle valve 5 to the idle or closed position. The position of the throttle valve 5 is detected by a throttle position sensor 17. An airflow sensor 62 detects the amount of air-intake to the engine 111. A acceleration pedal position sensor 61 detects the kick depth or the depression of the acceleration pedal 61a of the vehicle. An rpm sensor 110 detects the rpm of the engine 111. The outputs of the throttle position sensor 17, the airflow sensor 62, the acceleration pedal position sensor 61, the rpm sensor 110 are input to the control unit 8a which controls the operations of the throttle actuator 7, the injectors 112, and the ignition plugs 113,
FIG. 22 is a flowchart showing the control procedure followed by the vehicle control device of FIG. 21. The procedure of FIG. 22 is performed by the microcomputer within the control unit 8a. At step S31, the acceleration pedal position .alpha. is read in. Namely, the control unit 8a determines the acceleration pedal position .alpha. from the output of the acceleration pedal position sensor 61 which corresponds to the depression position of the acceleration pedal 61a. Next at step S52, the control unit 8a calculates the target throttle valve position .theta.s. The calculation is performed by: (1) determining a preliminary value of the target throttle valve position .theta.s using a relation between the acceleration pedal position .alpha. and the target throttle valve position .theta.s; and (2) multiplying the value obtained in (1) by a correction factor Ne. These steps are performed as follows.
The relation of the acceleration pedal position .alpha. and the target throttle valve position .theta.s depends on the output power performance of the vehicle with respect to the acceleration pedal position .alpha.. FIG. 23 shows the typical relation between the acceleration pedal position .alpha. and the target throttle valve position .theta.s. The curve a shows the relation according to which the target throttle valve position .theta. s is proportional to the acceleration pedal position .alpha.. 0n the other hand, the curve b shows the relation by which the target throttle valve position .theta.s increases slowly in the small depression range of the acceleration pedal position .alpha.. If the amount of air-intake varies greatly at the start or during the low speed range of the vehicle, there may be generated a shock and the fine adjustment of the power of the engine becomes difficult, The relation b in FIG. 23, is intended to resolve such problems.
FIG. 24 shows the relation between the rpm of the engine and the correction factor Ne (solid curve) and the relation between the rpm of the engine and the output torque of the engine (dotted curve). As shown by the dotted curve in FIG. 24, the output torque of the engine 111 does not remain constant over the whole range of the rpm of the engine. Namely, the output torque decreases in the, low and the high rpm region. If the target throttle valve position .theta.s as represented by the curve b in FIG. 23 is multiplied by the correction factor Ne which varies as indicated by the solid curve in FIG. 24, the output torque of the engine may be rendered substantially constant. The want of the output power felt by driver in the low and the high rpm region of the engine can thus be eliminated by multiplying the target throttle valve position .theta.s as represented by the curve b of FIG. 23 by the correction factor Ne shown in FIG. 24. It is noted that the relation of the target throttle valve position .theta.s with respect to the acceleration pedal position .alpha. of FIG. 23 and the relation of the correction factor Ne with respect to the rpm of the engine show the typical cases. These relations may be modified taking into consideration the characteristic of the vehicle or the output power performance of the engine. At step S32 in FIG. 22, the target throttle valve position .theta.s is calculated by multiplying the target throttle valve position .theta.s as determined by the relation b in FIG. 23 by the correction factor Ne shown in FIG. 24.
Further at step S33, the actual throttle valve position .theta.r is read in from the throttle position sensor 17. At step S34, the deviation e=.theta.s-.theta.r between the target throttle valve position .theta.s and the actual throttle, valve position .theta.r is calculated, and it is judged whether or not the deviation e is greater than 0. Namely, it is Judged whether or not the target throttle valve position .theta.s is greater than the actual throttle valve position .theta.r. If the target throttle valve position .theta.s is greater than the actual throttle valve position .theta.r, the execution proceeds to step S35, where the throttle actuator 7 is driven to rotate the throttle valve 5 toward the opening direction. On the other hand, if the target throttle valve position .theta.s is less than or equal to the actual throttle valve position .theta.r, the execution proceeds to step S36, where (provided that the target throttle valve position .theta.s is not equal to the actual throttle valve position .theta.r) the throttle actuator 7 driven to rotate the throttle valve 5 toward the closing direction.
As described above, in the case of the vehicle control device of FIG. 21, the throttle valve 5 is not mechanically linked with the acceleration pedal 61a, but is driven by the throttle actuator 7. The throttle valve 5 can thus be controlled with a higher degree of freedom. Further, by feeding back the vehicle speed signal to the engine control unit 8b, it is easy to provide the automatic cruising control. This electrical control of the throttle valve 5, however is not without disadvantage, Namely, since the throttle valve 5 is not mechanically linked with the acceleration pedal 61a, the throttle valve 5 may become inoperable due to a failure in the throttle actuator 7 or in the engine control unit 8b and the vehicle may run out of control. A fail-safe measure is thus indispensable.
FIG. 25 is a flowchart showing the fuel injection and the ignition operation of the vehicle control device of FIG. 21. Next, the operation of the vehicle control device of FIG. 21 upon occurrence of a failure is described by reference to FIG. 25
At step S41, the target air-intake a.sub.t is calculated on the basis of the acceleration pedal position .alpha. and the rpm of the engine. At step S42, the throttle actuator 7 is controlled to adjust the position of the throttle valve 5 such that the target air-intake a.sub.t is obtained. Next, at step S43, the actual air-intake a.sub.r is read in from the airflow sensor 62. At step S44, the deviation EQU .vertline.a.sub.t -a.sub.r .vertline.
between the target air-intake a.sub.t and the actual air-intake a.sub.r is calculated and it is judged whether or not the deviation .vertline.a.sub.t -a.sub.r .vertline. is greater than a predetermined reference level K. If the judgement is negative at step S44 (i.e., if .vertline.a.sub.t -.vertline.a.sub.r .vertline. is less than or equal to predetermined reference level K), the execution proceeds to step S48, where it is judged whether or not the throttle position sensor 17 is disconnected. The judment at step S48 is made, for example, on the basis of the output of the throttle position sensor 17. If the judgement is negative at step S48, the execution proceeds to step S49, where the normal fuel injection and ignition control operations are performed. Namely, the fuel is injected into all the cylinders, and the amount of injected fuel and the ignition timings are controlled on the basis of the outputs of the airflow sensor 62 and the rpm sensor 110 in accordance with the known method. On the other hand, if the judgement is affirmative at step S48, the execution proceeds to step S45. Further, if the judgement is affirmative at step S44 (if the deviation .vertline.a.sub.t -a.sub.r .vertline. is less than the predetermined reference level K), the execution proceeds directly to step S45.
At step S45, the acceleration pedal position .alpha. is read in from the acceleration pedal position sensor 61. At step S46, the number N=P(.alpha.) of the cylinders into which the fuel is injected is determined in accordance with the acceleration pedal position .alpha.. Further, at step S47 the ignition timings IG=q(.alpha.) are determined in accordance with the acceleration pedal position .alpha.. Thus, even when the throttle valve 5 cannot be driven due to a failure in the throttle valve control system, the fuel injection and the ignition are performed by the steps S45 through S47 in FIG. 25. Thus the vehicle control device provides a minimum drivability of the vehicle even upon an occurrence of a failure.
The method shown in FIG. 25 of engine control upon occurrence of a failure, however, has the following disadvantage. Namely, the procedure of FIG. 25 provides the drivability only if, upon occurrence of a failure, the throttle valve 5 is fixed at a position allowing at least a certain amount of air-intake. If the throttle valve 5 is at or near the idle or closed position upon occurrence of failure, it is impossible to obtain enough power and the vehicle can no longer be driven. On the other hand, if the throttle valve 5 is fixed at the fully open position upon occurrence of a failure, the output power of the engine may become too great even though the number of cylinders into which the fuel is injected is limited by the step S46. The safety of the driver may thus be at a risk,
FIG. 26 is a block diagram showing the overall structure of a conventional automatic cruising control unit. Within an air-intake pipe 3 is disposed a throttle valve 5 urged by a return spring 19 toward the idle or closed position. The operation of the acceleration pedal 61a or a vacuum actuator 55 is transmitted to a throttle link 50 via a pulley 51, such that the throttle valve 5 is driven toward the open position to allow greater amount of air-intake when the 61a or the 55 is operated. when both the acceleration pedal 61a and the vacuum actuator 55 are operated simultaneously to open the throttle valve 5, the operation or movement which is greater than the other is transmitted to the throttle link 50 through the pulley 51.
The automatic cruising control is effected by adjusting the position of the throttle valve 5 by means of the vacuum actuator 65. Next, the structure of the parts associated with the automatic cruising control is described.
A vacuum pump 58 generates a negative pressure for driving the vacuum actuator 55. A control valve 56 regulates the negative pressure generated by the vacuum pump 58. A release valve 57 completely coleases the negative pressure within to the ambient atmospheric pressure, and thereby stops driving the vacuum actuator 55. On the basis of the vehicle speed information obtained from a vehicle speed sensor 73, an automatic cruising control unit 70 controls the operations of the vacuum pump 58, the control valve 56, and the release valve 57 to adjust the position the throttle valve 5. To the automatic cruising control unit 70 are coupled various switches such as: a set switch 151 for instructing the commencement of the automatic cruising control, a resume switch 152 for instructing the restarting of the automatic cruising control at the vehicle speed set and stored in the automatic cruising control unit 70; a release switch 153 for instructing an interruption of the automatic cruising control; and a brake switch 154 linked with the brake of the vehicle for releasing the automatic cruising control upon detection of the operation of the brake.
FIG. 27 is a flowchart showing the automatic cruising control operation of the automatic cruising control unit of FIG. 26. FIG. 29 1s a timing chart showing waveforms of various signals generated in the vehicle control device of FIG. 26 during the automatic cruising control procedure. The top waveform shows the output of the set switch 151 by which the automatic cruising control is commenced. The waveforms thereunder are: the acceleration pedal position .alpha.; the actual throttle valve position .theta.r; the control signal for driving the release valve 57; the control signal for driving the vacuum pump 58; the control signal for driving the control valve 56; and the actual vehicle speed V.sub.A. On top of the waveforms are shown the corresponding steps S73 through S76 in the flowchart of FIG. 27.
At step S71 in FIG. 27, It is judged whether or not the commencement of the automatic cruising control has been instructed by the set switch 151. If the instruction is not present, the step S71 is repeated to wait for the input of the instruction. On the other hand, if the instruction is input from the set switch 151, the execution proceeds to step S72, where the current actual vehicle speed V.sub.A detected by the vehicle speed sensor 73 is stored as the target vehicle speed V.sub.T. Next, at step S73, the initial position of the throttle valve 5 is set as described below.
FIG. 28a shows the relation between the vehicle speed V and the initial position .theta. of the throttle valve for maintaining the vehicle speed V. FIG. 28b shows the relation between the target vehicle speed V.sub.T and the drive time T of the vacuum pump for attaining the initial throttle valve position .theta. as required by the relation of FIG. 28a, The vacuum pump 58 is supplied with an initial pulse (see the waveform in FIG. 29) such that it is driven for the time T corresponding to the target vehicle speed V.sub.T. The throttle valve 5 is thus adjusted to the initial position.
Next, at step S74, the throttle valve position is corrected. Namely, the deviation of the actual vehicle speed V.sub.A (detected by the vehicle speed sensor 73 after the initial pulse is output to the vacuum pump 58) from the target vehicle speed V.sub.T is calculated. To reduce the deviation, the correction pulses are supplied to the vacuum pump 58 (see the waveform for the vacuum pump 58 in FIG. 29), or the control valve 56 is opened intermittently, so as to correct the throttle valve position.
Further, at step S75, the feedback control of the throttle valve position is performed. Namely, the vacuum pump 58 is supplied with feedback pulses or the control valve 56 opened intermittently (see the waveforms for the vacuum pump 58 and the control valve 56 in FIG. 29) to adjust the throttle valve position such that the actual vehicle speed V.sub.A detected by the vehicle speed sensor 73 is controlled to the target vehicle speed V.sub.T. The feedback control is performed, for example, in accordance with the well-known PlD (proportional plus integral plus differential) control method.
At step S76, it is judged whether or not there is an occurrence of failure. Namely, it is judged whether or not the vehicle speed control has become infeasible due to an occurrence of failure in, for example, the throttle valve driving system. If the judgement Is affirmative at step S76, the execution proceeds to step S77, where the procedure tc deal with the occurrence of failure is performed. Namely, the control valve 56 and the release valve 57 are opened such that the throttle valve 5 is urged by the return spring 19 to the idle position and the safety of the driver is ensured.
On the other hand, if the judgement is negative at step S76, the execution proceeds to step S78, where it is judged whether or not the automatic cruising control is to be released. When an operation of the brake is detected from the output of the brake switch 154, or when the release of the automatic cruising control is instructed via the release switch 153, the judgement is affirmative at step S78, If the Judgement is negative at step S78, the execution returns to step S75 to repeat the step S75 through S78, On the other hand, if the judgement is affirmative at step S78, the execution proceeds to step S78, where the automatic cruising control is released. Namely, the control valve 56 and the release valve 57 are opened such that the throttle valve 5 is urged by the return spring 19 to the idle position. After step S79, the execution returns to step S71, where the execution sits on a loop waiting for the next commencement of the automatic cruising control.
The above automatic cruising control device of FIG. 26, however, has the following disadvantage. Although the throttle valve 5 is driven toward the opening direction by the vacuum actuator 55 and hence the "open failure" of the throttle valve due to an occurrence of failure in the vacuum actuator 55, the control valve 56, and the release valve 57 is rare, the throttle valve 5 is returned to the idle position solely by the action of the return spring 19. When the automatic cruising control is to be released, the control valve 56 and the release valve 57 are opened to release the negative pressure within, such that the throttle valve 5 is closed by the action of the return spring 19. Thus, if the shaft of the throttle valve 5 or the throttle link 50 is stuck upon biting in a foreign material into the mechanical driving parts thereof, the urging force of the return spring 19 may prove insufficient for returning the throttle valve 5 to the idle position. Then, the rpm of the engine may rise unduely against the intention of the driver. The vehicle may thus run out of control and present a grave danger to the safety of the driver.